35 years of life expectancy was not reality. If you lived past childhood you usually lived until your 50s or 70s. There are tribal villages in africa today that barely have modern anything and have many people in their 90s. Human life expectancy decreased with the transition from hunter/gatherer/herder tribes into agriculture with a few crops, due to relative malnutrition. It's only recently in modern times that we have started matching hunter gatherer life expectancy with our knowledge of nutrition and 120 year old medical knowledge.
>35 years of life expectancy was not reality
So? That's still the definition of life expectancy. Moreover, being able to live to 90 if everything went right doesn't mean much when you die at 20 because of a treatable illness/injury, or seeing your wife/kid die in childbirth.
Yes, we'd be much better off if we'd just stop progressing at some arbitrary point, and just accepted:
- 35 years of life expectancy
- no running water
- famines every decade
- zero modern technology, like electricity or even healthcare